Uses of Resistors and Capacitors

Limit current (Resistances)

The current passing through a component multiplied by the voltage determines the power it consumes in Watts W.

If we want to limit the current that passes through an electronic track, such as the communication of a sensor with a control microchip, a resistance is placed so that the current is determined by the voltage divided by the resistance. We will do this to protect electronic devices from overly large currents, which destroy them instantly.

Wired digital communications and inputs such as buttons and rotary encoders require pull-up and pull-down resistors to ensure high and low states.

Pull-up and Pull-down (Resistances)

Digital communications, both those that connect “external” devices such as USB and internal ones such as I2C, are made through data buses.

Those digital buses are tracks that connect one device to the other and, often, to a set of devices with each other. Since digital communications are made with ones and zeros, these in physical reality are respectively high and low voltages as each standard has defined.

For example, the low-speed USB standard has two D + and D- lines on the data bus. To transmit a 1, put 2.8 V on D + with a 15 K resistor to ground (0V) and 0.3 V on D- with 1.5 K to positive (3.3 V). To transmit a 0, there is a D + less than 0.3 V and a D- greater than 2.8 V, both having the pull-down and pull-up resistors respectively. The receiving device compares the voltages and detects what it has received.

Those 15K resistors in pull-down and 1.5K in pull-up ensure that after a voltage change the level is maintained. Without them, the devices would not be able to maintain them and the voltage would fluctuate and pulse, so the communication would get dirty and errors would prevent the correct connection.

Low Energy Instant Storage (Capacitors)

In very varied applications we may be interested in storing a small amount of energy in an electronic design.

When there is a momentary loss of energy in the supply of a chip, it loses its state and its operation throughout the device is wrong. If we place a capacitor in the supply track, during the moments that the loss may last we can maintain the internal states.

Filters allow only frequencies greater than, less than, or between two defined values to pass.

Frequency filters (Resistors and Capacitors)

Although filters can also be made by coils, they are usually made up of resistors and capacitors.

At each point of the electronic circuit we are interested in having only the frequencies included in a range, according to the intent of the track. In a power track we will only want zero frequency direct current. On a communication track, we want to eliminate all direct current and only have high frequencies.

In order to filter with higher quality, higher order filters are used, with operational amplifiers, but in many cases, the zero order filters that only use resistors, capacitors and diodes if this is the case.

conclusion

Although when you have experience in electronic design it is possible to identify what function electronic components fulfill, for example in a motherboard, it is not our intention to teach in order to compare the quality between the models and others based on this.

With what we have explained in this publication the reader must understand that in addition to GPU chips, RAM, controller, etc., simple components such as resistors and capacitors also play a very important role in the good performance and robustness of a device such as an SSD or a graphics card.

For this reason, when talking about the quality of one brand or model over another, good electronic design does not condition but determines whether it will cause problems or not and that its performance will be higher or lower.